$(select).val().length of null 给出错误

Question

我的表单中有一个 select 对象，其样式使用 Bootstrap-select.js 插件。当我初始化 select 框并尝试获取它的值时，它是 null 直到我 select 一个选项。在我的脚本中，我使用的是：-

$(select).val().length

但是，当 $(select).val() 为 null 时，这会出错。我真的很想得到一个 0.

我该怎么做？

Answer 1

试试这个

function get_length( select ){
 if ( $(select).val() != null ) {
  return $(select).val().length;
 }else{
  return 0;
 }
}

console.log( get_length(my_select_box_variable) );

Answer 2

使用这个。

var $selectElement = $("#mySelect");
var len = $selectElement.val() != null ? $selectElement.val().length : 0;
console.log(len);

Answer 3

尝试：-

($(select).val() || '').length

Logical Operators

Logical operators are typically used with Boolean (logical) values. When they are, they return a Boolean value. However, the && and || operators actually return the value of one of the specified operands, so if these operators are used with non-Boolean values, they may return a non-Boolean value.

Examples of expressions that can be converted to false are:

null

NaN

0

empty string ("")

NaN

undefined

演示

var length = ($('select').val() || '').length;

console.log('length: ' + length);

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>

<select>

<select>

$(select).val().length of null 给出错误

$(select).val().length of null gives error

jquery

bootstrap-select